Sergeant Rick Clements suffered devastating injuries when he stepped on a Taliban bomb while leading a foot patrol in southern Afghanistan. He lost both legs, severely damaged an arm, suffered terrible internal injuries and was told that he could never have children or a sex life.

Doctors told him that two years ago he would probably not have survived.

But as he underwent intensive rehabilitation at Headley Court, the military rehabilitation centre in Surrey, there came a fresh blow.

In a four-page letter from the Armed Forces Compensation Scheme, Ministry of Defence officials told him, in graphic detail, exactly how much compensation he was entitled to for each injury, and said he should be paid £633,025.

But, wrote an anonymous civil servant, he would receive only £575,000.

"We have paid you this amount because the scheme rules say that where more than one injury is sustained in one incident, the total amount shall not exceed the amount payable under tariff 1," the letter said.

Sgt Clements had fallen foul of a "tariff", a cap on total payments made to wounded soldiers, a measure designed to contain the cost to the public purse, albeit a limit which was doubled three years ago.

If he had suffered his injuries as a civilian, he could have expected £4 million in compensation - and in contrast a clerk working for the RAF received £484,000 after suffering a damaged thumb while typing computer data.

But because he was wounded by a hidden improvised explosive device during a foot patrol close to the town of Nad e'Ali in central Helmand, just a week into a six-month tour of duty, his payment will be far lower.

Now the 31-year-old soldier is attempting a legal challenge to the payment, which equates to an index-linked income of £2,000 a month for life, which must pay for his care.

"I was devastated," he said.

"I just thought why send it [the letter], why tell me that I should be getting a certain amount but it was going to be capped at a lower level. Imagine how that feels when you are in recovery? It can't be right."

Despite his injuries, he and his fiancee, Leanne Isaacs, 28, who is his full-time carer, still plan to marry in June this year after he is discharged from the 2nd battalion Duke of Lancaster's Regiment.

He made the deeply personal decision to break a taboo among soldiers by speaking of how the loss of his testicles means he cannot have children.

In an exclusive interview with The Sunday Telegraph, he said: "No one in the Army wants to talk about losing your testicles when you get blown up - it's taboo.

"I think the Army are worried that it might put people off joining. But guys should know that this can happen and know what sort of compensation you will get and how tough life will be.

"I'm not the first and I won't be the last. I wish someone had told me to make a sperm donation before I had gone to Afghanistan. Had they done so then I would have been able to have children."

His fiancee, Leanne Isaacs, 28, added: "Rick will never have a normal life. He can't have kids, he can't have sex again, he can't have a normal relationship. If he ever can walk again, it won't be for more than an hour a day.

"I can't see how they can justify the amount he has been given. He has given everything to his country and the government won't even pay the amount he is entitled to. It makes me very angry.

"No amount of money can compensate Rick for what he's lost but surely they can do better than this. It's disgusting, it's unfair.

"The people who make these decisions should come out and see the type of injuries soldier's like Rick have. No one has come to see us."

Sgt Clements said: "After things settled down, I realised that I wasn't going to be able to have children or have a sexual relationship with Leanne and that is very difficult.

"It is also going to be very difficult for me to walk again, especially because on my left hand side the amputation goes right the way up and my other stump is very small.

"The worst thing is seeing the effect my injuries have had on Leanne and the rest of my family. I feel sometimes that I have ruined their lives more than my own.

"I have days when I feel very low and there have been times when I think that I would have been better off dead.

"You wonder "why you" and you look at all the decisions you made on that day and even why you joined the Army but those feelings don't tend to last long. But I was in charge that day - there is no one else to blame. I made all the decisions

"But I try to look on the bright side - I'm still alive and I've got Leanne."

Leanne, who is a trained carer has two children aged six and nine from a previously relationship, added: "When I was told of Rick's injuries I thought he was going to die and my only thought was to get him back to England as quickly as possible so his family can be with him.

"I thought if he is going to die then I want to be with him. I didn't want him to die on his own.

"It didn't ever enter my mind that I would ever leave him because of his injuries - he's still Rick. He is quieter now, a bit more subdued but he is still Rick.

There have been some tough times and there will be tough times ahead, we know that but we will get through them."

It is a measure of Sgt Clements' fortitude that despite his injuries he still counts himself lucky when compared to some injured soldiers.

"I've seen guys with sever facial injuries, brain injuries and one soldier who can't talk. The doctors told me that my injuries are some of the worst they've had and if I have been wounded two years ago I wouldn't have survived."

Hilary Meredith, the solicitor acting for Sgt Clements said: "Soldiers in particular often suffer multiple injuries in one incident. The tariff seeks to award 100 per cent for the first main injury and then reduced each further injury on a sliding scale.

"This results in the unsatisfactory knowledge that 100 per cent entitlement for each specific injury can never be achieved.

"To make matters worse the whole award is then capped at £570,000, a very small amount to look after a young soldier for life, often medically discharged into civvy street with no future earning capacity and a meagre pension."